From: "Russ Cox" <rsc@swtch.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] fun and scary evil C code
Date: Wed, 19 Dec 2007 15:37:25 -0500 [thread overview]
Message-ID: <20071219203654.3714F1E8C1C@holo.morphisms.net> (raw)
In-Reply-To: <3e1162e60712190715q3f50d601sd88b1e0c6c74afc8@mail.gmail.com>
> #define TRIO_DOUBLE_INDEX(x) (((unsigned char *)&internalEndianMagic)[7-(x)])
this is actually done in /sys/src/9/port/devcons.c too:
static uvlong uvorder = 0x0001020304050607ULL;
static uchar*
le2vlong(vlong *to, uchar *f)
{
uchar *t, *o;
int i;
t = (uchar*)to;
o = (uchar*)&uvorder;
for(i = 0; i < sizeof(vlong); i++)
t[o[i]] = f[i];
return f+sizeof(vlong);
}
static uchar*
vlong2le(uchar *t, vlong from)
{
uchar *f, *o;
int i;
f = (uchar*)&from;
o = (uchar*)&uvorder;
for(i = 0; i < sizeof(vlong); i++)
t[i] = f[o[i]];
return t+sizeof(vlong);
}
presotto wrote the code but said he learned the trick from ken.
there, of course, we have a real compiler and don't have to
write uvlong constants as floating point numbers
(wow that seems fragile).
russ
next prev parent reply other threads:[~2007-12-19 20:37 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-19 15:15 David Leimbach
2007-12-19 20:37 ` Russ Cox [this message]
2007-12-19 22:32 ` Robert William Fuller
2007-12-19 22:38 ` erik quanstrom
2007-12-19 22:51 ` Bakul Shah
2007-12-20 0:18 ` dave.l
2007-12-20 0:33 ` dave.l
2007-12-20 0:51 ` erik quanstrom
2007-12-20 9:29 ` roger peppe
2007-12-20 13:02 ` erik quanstrom
2007-12-20 16:29 Russ Cox
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